The introduction of mobile communications systems in which subscribers access the system on demand via a wireless link has introduced the attendant need for authentication procedures to ensure that a handset is genuine and that the user is entitled to use the system facilities. There is also a need for system security to prevent ‘eavesdropping’ of the wireless signals e.g. to prevent theft of a subscriber identity and subsequent fraudulent use of the system.
The proliferation of wireless communications systems and the introduction of third generation (3G) networks, also referred to as the Universal Mobile Telecommunications System (UMTS), has increased the system security requirements. These requirements include not only the authentication by the network that the mobile is entitled to access the network, but also an authentication by the mobile that the network to which it is trying to connect is authorised to deliver the services as defined by the mobile user's service provider. Part of this authentication procedure involves the exchange between the mobile and the network of secret key information known only to the network and that particular mobile. As an additional security feature, this key information is changed each time the mobile accesses the network. This process requires the calculation of sequence numbers which are used to construct authentication vectors.
A description of the security architecture for the Universal Mobile Telecommunications System is given in publicly available standards documents ETSI TS 133.102 v.3.1 and v.3.9, the contents of which are incorporated herein by reference.
Network security is an issue that is currently under review, and the relevant standards are thus continually evolving. As a consequence, it has been found that the currently established methods of sequence number generation are less than optimum and are not fully compatible with the more recent standards, nor with the commonly used Supercharger functionality.